The present invention relates generally to oil seals and sealed mechanisms, and more particularly, to oil seals which are retained in position on their inside diameter on a longitudinally movable rod or rack, and which have two oppositely directed sealing lips on their outside diameter. The seal thus also acts as a piston in this application. The application for such seals is primarily as an improvement in seals used to isolate two separate but variable volume chambers in a power steering system.
The present practice in a power steering application is to have a movable rack with an intermediate portion which is operated by a pinion, with either end of the rack serving to move the steering arms of a vehicle. The rack itself is moved by hydraulic force exerted to either side of the seal or piston, with the force being created by the power steering pump. The power steering module includes a sealed housing surrounding this rack, and the housing includes two pressure ports, one on either side of the seal. Depending on which side of the seal is pressurized, the seal, and hence the rack, is pushed to one side or the other in keeping with the desires of the operator. The rack is also sealed with auxiliary seals at both ends, since the rack as a whole must move back and forth with respect to the sealed cavity.
In a typical application, which includes a rack longitudinally movable within the housing (laterally as respects the vehicle), it is desired to subdivide the hollow annular space between the housing and the rack into two chambers by means of a seal or piston which effectively keeps the chambers separate and which also, when acted upon by the hydraulic force generated by the power steering pump, moves the rack in either direction, depending upon the side, if any, which is pressurized.
The typical seal presently used in this application is a four element seal, including a one piece forging, which includes a body having an extended steel nose portion, a formation that retains a steel ring in a first groove on the rack, an o.d. seal-receiving groove, and a tail portion of reduced thickness which is permanently swaged or staked into a second groove in the rack. The steel ring and the swaged end forced into the second groove cooperate to locate the body on the rack and keep it from moving in either direction.
The o.d. seal-receiving groove in the forged body includes an interior elastomeric O-ring and an exterior PTFE or xe2x80x9cTeflonxe2x80x9d ring of rectangular cross-section engaging the cylindrical wall of the housing. The rubber O-ring supplies a radially outward load to the PTFE ring. The forging o.d. is very close to the bore, but does not contact it. The nose portion of the forging is used one time only to seat a seal in a counterbore in the closed end portion of the housing.
In use, several disadvantages of this type of rack seal exist. The first is the matter of cost. Because the principal portion of the seal is a forging, it costs more than a stamping or part made from sheet metal. However, it is thought to be necessary because of the fact that it positively locates the O-ring and PTFE member. This requires very fine tolerances in the dimension of the groove. One problem with the PTFE outer seal is that it tends to extrude through the gap between the forging and the cylindrical surface of the housing, especially after a time and in the presence of high pressure hydraulic loads. The O-ring may take a compression set after a time and thus tend to aggravate this problem. Another difficulty is that of quality, with one supplier being used for the rubber and PTFE elements, and another for the forged components.
Accordingly, in view of these and other disadvantages and shortcomings of the prior art, it would be advantageous to provide an improved seal for this and other related applications. For example, it would be also advantageous, if possible, to use a stamping as the casing unit in place of the forging presently used. It would be also advantageous if a twin lip seal could be applied to the stamping in a single operation to create two oppositely facing primary sealing lips.
Another advantage would be to provide a readily deformable flange on a stamping which could be swedged or staked into the groove on the rack shaft. Still further, another advantage would be, in one embodiment, to create an integral rubber formation which could accommodate a snap-in plastic nose portion for seating an auxiliary seal which is required on the xe2x80x9cblindxe2x80x9d end of the housing. It would be advantageous if the stamping could have a rolled or otherwise formed groove in the casing to engage the retainer ring and insure that the casing unit maintained its position on the rack.
In view of the shortcomings of the prior art, it is therefore an object of the present invention to provide an improved, new design for a steering rack seal.
Another object of the present invention is to provide a seal or piston which utilizes bonded two rubber lips as the primary seal members.
A still further object of the invention is to provide a seal or piston which is secured by two different means to the rack and which contains a casing made from a stamping or drawing rather than a forging.
Still another object of the invention is to provide a dual lip seal which, on the inside surfaces of the lips, contains a contoured or beaded portion.
Yet another object of the invention is to provide a seal with a pair of lips separated by a center portion, with the center portion having beads extending radially outwardly on its outer diameter surface.
A further object of the invention is to provide a seal which includes an installation nose in the form of a snap-in plastic ring fitting in a groove in the intermediate diameter of the seal and engaging portions of the seal lip body spaced from the sealing lips proper.
A still further object of the invention is to provide the seal with dual sealing lips and also containing an elastomeric seal body which includes an inside diameter cylindrical surface, which surface is adapted for an interference fit with a metal casing extending axially outwardly thereof and serving to act as the nose portion for installing an auxiliary seal.
Another object of the invention is to provide a seal with a nose portion made from a folded over portion of the casing and on which the outside diameter of the casing has bonded to it a seal body with a dual lip configuration.
Still another object of the invention is to provide a seal with a casing having one end with a tail portion adapted to be pressed into a groove on the rack, an intermediate portion having a bright portion which also serves as the bonding portion for a dual lip peripheral seal and still further includes an axially extending portion serving to engage and seat an auxiliary seal.
These and other objects and advantages of the invention are achieved in practice by providing an improved seal or piston unit for a rack or other movable rod, the seal including a tail portion adapted to be swaged into a groove in the rack or rod, a dual lip seal portion bonded to a part of the casing, a groove in the casing for accommodating a retainer ring, and, in several embodiments, various forms of an integral or separable nose portions to assist in installing another auxiliary seal in the application.
The manner in which these and other objects are achieved in practice will become more fully apparent when considered in conjunction with a description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, in which like reference numbers indicate corresponding parts throughout.